Present day engines are being manufactured to produce a compact package offering improved fuel economy, longer service life, and greater power output per cylinder. The engines are constantly being upgraded in order to accomplish these goals thereby subjecting the piston assemblies to higher combustion chamber pressures and temperatures. It is for that reason that emphasis has been placed over the past several years on finding new and economical means to manufacture a piston assembly capable of withstanding these higher combustion chamber pressures and temperatures.
The goal of the prior art piston assemblies was to provide economical piston assemblies by reducing excessive weight and limiting structural components. The prior art piston assemblies included a two piece articulated piston assembly with a wrist pin attached to an upper piston member, resulting in reduced piston assembly weight, a simplified skirt or crown geometry, and improved manufacturability. However, the wrist pin is attached to the piston member by extending a bolt through the wrist pin and into the upper piston member on opposing sides of the connecting rod. Due to the high combustion pressures experienced during operation of present day engines, the bolting pattern and loading design of the prior art allows the wrist pin to flex about the central axis of the piston assembly causing ultimate failure of the design. Required bolt access on the piston underside also limits the connecting rod bearing length, and thereby, piston load capacity.
In other prior art piston assemblies, the wrist pin is attached to the connecting rod by bolts extending through the connecting rod into the wrist pin. A pair of struts or connecting members extend from an upper piston member and surround the wrist pin making a more complicated and expensive part to manufacture.
Another example of a piston assembly is disclosed in U.S. Pat. No. 1,810,423 issued to Roscoe J. Hatch on Jun. 16, 1931 wherein a one piece piston assembly has the piston member attached to the wrist pin by extending bolts through the piston member and into the wrist pin on opposing sides of the connecting rod. This prior art design may experience flexing of the wrist pin about the central axis of the piston assembly due to the bolting pattern and loading design. In addition, the one piece design results in a longer and more complicated piston assembly resulting in more costly manufacturing. Furthermore, the piston assembly disclosed by Hatch is made from aluminum with small bearings designed for the automotive industry. Therefore, the piston assembly would not withstand the pressures necessary for present day heavy duty diesel engines.
In another example, UK Pat. No. GB2,198,210A issued to Michael Ledsham Price Rhodes on Jun. 8, 1988, discloses a piston assembly. The piston having a bifurcated connecting rod and a piston member which has a central boss and two outer bosses which contact the wrist pin on three mounting surfaces. However, the one piece design results in a longer and more complicated piston assembly including a pair of struts or connecting members which surround the wrist pin resulting in increased weight for the piston assembly. The longer one piece design, including the pair of struts, is more complicated and expensive to manufacture. Furthermore, as with Hatch, the piston assembly disclosed by Rhodes is made from aluminum with small bearings designed for the automotive industry. Therefore, the piston assembly would not withstand the pressures necessary for present day heavy duty diesel engines.
The present invention discloses an attachment method which provides an inexpensive, compact design for maximum load capacity without complicated manufacturing and machining requirements. The present invention also increases the bearing area across the wrist pin increasing overall stability and reliability of the piston assembly.